Optical recording medium

ABSTRACT

An optical recording medium is provided in which a recording layer contains a salt-forming dye between an ion of an azo metal complex of the following formula (I) and an ion of a cyanine dye of the following formula (II), having a complex index of refraction in the wavelength region of recording light and/or reading light whose imaginary part k is up to 0.20, or at least one of azo oxovanadium metal complexes having an azo compound of the following formula (III) as a ligand and metal complexes having azo compounds of the following formulae (IV) and (V) as a ligand. Recording and reading can be carried out at a conventional wavelength or a short wavelength of about 630-690 nm or both.                    
     In formulae (I) and (III), A is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group or a nitrogenous heteroaromatic ring group having an oxovanadium-coordinatable nitrogen atom at a position adjacent to the carbon atom in the ring attached to the diazo group, and B is an aromatic ring group having an active hydrogen-bearing group at a position adjacent to the diazo group. In formula (I), m is equal to 1 or 2, and M 1  is a center metal. 
     In formula (II), Q 1  and Q 2  each are a group of atoms forming a 5-membered nitrogenous heterocyclic ring which may have a fused ring, L is a methine chain, R 1  and R 2  each are an alkyl group. 
     In formulae (IV) and (V), X is an active hydrogen-bearing group, R 1  and R 2  each are an alkyl group, the total number of carbon atoms in R 1  and R 2  is from 2 to 8, R is a nitro group, and n is equal to 0 or 1.

TECHNICAL FIELD

This invention relates to an optical recording medium and moreparticularly, to a highly light resistant optical recording mediumcapable of writing and reading with a near-infrared laser of 770 to 830nm, an optical recording medium capable of writing and reading with ared laser of 630 to 690 nm, or an optical recording medium capable ofwriting and reading with a near-infrared laser of 770 to 830 nm and ared laser of 630 to 690 nm.

BACKGROUND ART

The present inventors have been engaged in the development of write-oncetype compact discs (CD-R) as a recordable optical recording mediumcorresponding to the compact disc (CD) standard.

As the dye for the CD-R's, cyanine dyes have been widely employedbecause of their solubility and wavelength characteristics. The cyaninedyes, however, have the drawback of poor light resistance or fastness.As a solution to this problem, attempts have been made to add quenchersand to form salts with Ni and Cu dithiolene metal complexes. Thesemethods leave the problems that light resistance is not fully improvedand productivity is low on account of poor solubility.

Under such circumstances, JP-B 37580/1995 proposes an optical recordingmedium comprising a chromium-containing azo compound. This medium,however, is insufficient in light resistance. JP-B 37580/1995 alsodiscloses an optical recording medium comprising a cyanine dye and anazo metal chelate compound of an azo compound with a metal. Further,JP-A 55189/1990 discloses an optical recording medium comprising arecording layer composed of a cyanine dye and a diol hexa-coordinatemetal complex salt compound of naphthalenino-azobenzene. Mixtures of acyanine dye and an azo metal compound as used in these examples provideinsufficient light resistance. Also, JP-A 51182/1991 discloses anoptical recording medium comprising on a transparent substrate arecording layer containing a photo-stabilized organic dye in the form ofa bonded compound of an anion of an electron-accepting azo metal complexsalt compound with a cation of a cyanine dye having absorption in thewavelength region of recording light. However, neither the cyanine dyecation nor the compound bonded therewith is specified therein, and thedesired characteristics are not obtained when certain cyanine dyecations are combined. The only exception is FIG. 2 showing theabsorption spectrum of a recording layer. But we confirmed that nosatisfactory characteristics were obtained when such a dye was appliedto CD-R.

Higher density optical recording media are desired in the recent years.Exemplary media are CD-R of the next generation wherein the recordingwavelength of CD-R is reduced from the current 780 nm to a shorterwavelength of 680 nm to 635 nm and write-once type digital video discs(DVD-R) capable of recording and reading at 650 nm. With theinterchangeability with the existing CD-R taken into account, CD-RIIcapable of reading at a short wavelength too has been proposed. Therequirements on the dyes used in these standards are consideredsubstantially equal to those on the currently used dyes except thewavelength. However, since development works have hitherto been made soas to match with 780 nm, there are known few dyes which can satisfydesired characteristics including light resistance, solubility andrecording sensitivity on the shorter wavelength side of 680 nm to 635nm.

For use in recording layers of optical recording media adapted to recordsignals at a laser wavelength of 680 nm to 635 nm, mention may be madeof cyanine dyes, which undergo substantial photo-degradation and lackstability. Dyes having higher light resistance include metal azocomplexes as described in JP-B 51682/1995, JP-A 268994/1991, and JP-A156408/1996, for example. Despite high light resistance, these dyes havethe problems of low recording sensitivity and low solubility, and thatwhen used in optical recording media, the dyes fail to afford a goodbalance between Rtop and modulation among disc characteristics onaccount of a broader half band width of their absorption spectrum.

DISCLOSURE OF THE INVENTION

A primary object of the invention is to provide an optical recordingmedium which has improved light resistance and a sufficient solubilityin coating solvents which do no attack polycarbonate substrates,especially fluorinated alcohol solvents and cellosolve solvents capableof improving a tact time, and exhibits excellent recording/readingcharacteristics complying with the CD standard to light having awavelength selected from the range of 770 nm to 830 nm, especially awavelength of 780 nm. A second object is to provide an optical recordingmedium which has improved light resistance and exhibits excellentrecording/reading characteristics at a wavelength selected from therange of 630 nm to 690 nm, especially 635 nm to 680 nm; and a thirdobject is to provide an optical recording medium which, in addition tothe above advantages, exhibits excellent recording characteristicssufficient to enable recording and reading in accordance with the CDstandard, with light having a conventional wavelength selected from therange of 770 nm to 830 nm, especially a wavelength of 780 nm.

This and other objects are achieved by the present invention which isdefined below as (1) to (17).

(1) An optical recording medium comprising a recording layer containinga salt-forming dye between an ion of an azo metal complex of thefollowing formula (I) and an ion of a cyanine dye of the followingformula (II), the salt-forming dye having a complex index of refractionin the wavelength region of recording light and/or reading light whoseimaginary part k is up to 0.20;

wherein in formula (I), A is an aromatic ring group having an activehydrogen-bearing group at a position adjacent to the diazo group or anitrogenous heteroaromatic ring group having therein a metalion-coordinatable nitrogen atom at a position adjacent to the carbonatom in the ring attached to the diazo group; B is an aromatic ringgroup having an active hydrogen-bearing group at a position adjacent tothe diazo group; m is equal to 1 or 2; and M₁ is a center metal, withformula (I) schematically illustrating the coordination of A—N═N—Bthereto;

in formula (II), Q¹ and Q² each are a group of atoms forming a5-membered nitrogenous heterocyclic ring which may have a fused ring; Lis a methine chain; R¹ and R² each are an alkyl group.

(2) The optical recording medium of (1) wherein in formula (II), thenitrogenous heterocyclic ring completed by Q¹ or Q² which may have afused ring is an indolenine ring, thiazoline ring or oxazoline ring, andL is trimethine or pentamethine.

(3) The optical recording medium of (1) or (2) wherein the ion ofcyanine dye of formula (II) is an ion of an indolenine type cyanine dye.

(4) The optical recording medium of any one of (1) to (3) wherein thecenter metal represented by M₁ in formula (I) is vanadium, cobalt,nickel or copper.

(5) An optical recording medium comprising a recording layer containingan azo oxovanadium metal complex between an azo compound of thefollowing formula (III) and oxovanadium;

A—N═N—B  (III)

wherein A is an aromatic ring group having an active hydrogen-bearinggroup at a position adjacent to the diazo group or a nitrogenousheteroaromatic ring group having therein an oxovanadium-coordinatablenitrogen atom at a position adjacent to the carbon atom in the ringattached to the diazo group; and B is an aromatic ring group having anactive hydrogen-bearing group at a position adjacent to the diazo group.

(6) The optical recording medium of (5) wherein A in formula (III) is anaromatic ring group having an active hydrogen-bearing group at aposition adjacent to the diazo group.

(7) An optical recording medium comprising a recording layer containingan azo metal complex obtained by combining at least one of an azocompound of the following formula (IV) and a compound of the followingformula (V) with a metal compound;

wherein X is an active hydrogen-bearing group, R¹ and R² each are analkyl group, the total number of carbon atoms in R¹ and R² is from 2 to8, R is a nitro group, and n is equal to 0 or 1.

(8) The optical recording medium of (7) wherein said azo metal complexis a metal complex with oxovanadium or cobalt.

(9) The optical recording medium of (7) or (8) wherein said azo metalcomplex is a metal complex of the compound of formula (V) withoxovanadium or cobalt.

(10) The optical recording medium of any one of (5) to (9) wherein saidrecording layer contains a second light-absorbing dye having differentoptical properties from said azo metal complex, and recording/readingoperation is carried out with light having a first wavelength of 630 to690 nm and light having a second wavelength of 770 to 830 nm.

(11) The optical recording medium of (10) wherein recording is carriedout with light having the second wavelength and reading is carried outwith light having the first and second wavelengths.

(12) The optical recording medium of (10) wherein said recording layeris disposed on a substrate, in which said azo metal complex has acomplex index of refraction at 650 nm whose real part n is 1.8 to 2.6and whose imaginary part k is 0.02 to 0.20, and said secondlight-absorbing dye has a complex index of refraction at 780 nm whosereal part n is 1.8 to 2.6 and whose imaginary part k is 0.02 to 0.30 andforms a thin film whose absorption spectrum has a half band width of upto 170 nm.

(13) The optical recording medium of any one of (5) to (9) wherein therecording layer is constructed of at least two layers by laying on afirst recording layer containing said azo metal complex a secondrecording layer containing a second light-absorbing dye having differentoptical properties from said azo metal complex.

(14) The optical recording medium of (13) wherein said azo metal complexhas a complex index of refraction at 650 nm whose real part n is 1.8 to2.6 and whose imaginary part k is 0.02 to 0.20, and said secondlight-absorbing dye has a complex index of refraction at 780 nm whosereal part n is 1.8 to 2.6 and whose imaginary part k is 0.02 to 0.15 andforms a thin film whose absorption spectrum has a half band width of upto 170 nm, and the recording layer constructed of at least two layers isdisposed on a substrate.

(15) The optical recording medium of (13) or (14) wherein the firstrecording layer is disposed on the substrate, and the second recordinglayer is disposed on the first recording layer.

(16) The optical recording medium of any one of (10) to (15) whereinsaid second light-absorbing dye is a phthalocyanine dye of the followingformula (VI):

wherein M is a center atom; X₁, X₂, X₃, and X₄, which may be the same ordifferent, are halogen atoms; p1, p2, p3, and p4 are 0 or integers of 1to 4, p1+p2+p3+p4 is equal to 0 to 15; Y₁, Y₂, Y₃, and Y₄, which may bethe same or different, are oxygen atoms or sulfur atoms; Z₁, Z₂, Z₃, andZ₄, which may be the same or different, are alkyl groups having at least4 carbon atoms, alicyclic hydrocarbon groups, aromatic hydrocarbongroups or heterocyclic groups; q1, q2, q3, and q4 are 0 or integers of 1to 4, they are not equal to 0 at the same time, and q1+q2+q3+q4 is equalto 1 to 8.

(17) The optical recording medium of (15) or (16) wherein said firstrecording layer and said second recording layer each have a thickness of20 to 250 nm, and the thickness of said first recording layer divided bythe thickness of said second recording layer is from 0.1 to 1.

It is noted that JP-A 51182/1991 discloses an optical recording mediumcomprising on a transparent substrate a recording layer containing aphoto-stabilized organic dye in the form of a bonded compound of ananion of an electron-accepting azo metal complex salt compound with acation of a cyanine dye having absorption in the wavelength region ofrecording light. However, this patent lacks the description specifyingthe cyanine dyes or the compounds bonded therewith, and refers nowherethe imaginary part k of the complex index of refraction of the bondedcompounds.

JP-A 156408/1996 discloses an optical recording medium comprising arecording layer containing a metal complex of an azo compound and a dyehaving substantial absorption at 720 to 850 nm, and describes that it iscapable of recording and reading with light of 780 nm and also capableof reading or recording and reading with light of 620 to 690 nm.

Although the azo compounds disclosed therein are encompassed within theazo compounds of formula (III) according to the present invention, thecenter metals of the metal complexes are Ni, Co, Pd, etc. No referenceis made to oxovanadium (VO) according to the present invention.

Also, the azo compounds disclosed therein have a nitrogenousheterocyclic ring as one of the rings connected through the diazo group,and their structure is apparently different from formulae (IV) and (V)defined in the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating how to determine a half band width froman absorption spectrum of a thin film of phthalocyanine dye.

FIG. 2 is a fragmental cross-sectional view of an optical disc accordingto one embodiment of the invention.

FIG. 3 is a fragmental cross-sectional view of an optical disc accordingto another embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now the present invention is described in detail.

The optical recording medium of the invention has a recording layerwhich contains an azo family metal complex compound. The azo familymetal complex compound is a salt-forming dye between an ion of an azometal complex of formula (I) and an ion of a cyanine dye of formula(II), an azo oxovanadium metal complex of an azo compound of formula(III) with oxovanadium, or an azo metal complex obtained by reacting atleast one of azo compounds of formulae (IV) and (V) with a metalcompound.

The salt-forming dye is used, mainly by virtue of a choice of thecyanine dye skeleton, for the purpose of recording and/or reading in theshort wavelength region of 630 to 690 nm or for the purpose of recordingand/or reading in the conventional wavelength region of 770 to 830 nm.The azo oxovanadium metal complex and the azo metal complex are used forthe purpose of recording and/or reading in the short wavelength regionof 630 to 690 nm.

First of all, the salt-forming dye is described.

The salt-forming dye has a complex index of refraction in the wavelengthregion of recording light and/or reading light whose imaginary part k isup to 0.20, preferably 0 to 0.20, and more preferably 0.01 to 0.20. Byrestricting k in this range, the dye is given a sufficient reflectanceto ensure effective recording and reading. In contrast, if k exceeds0.20, the reflectance becomes insufficient. Herein, the real part n ofthe complex index of refraction is preferably at least 1.8, and morepreferably 1.8 to 2.6. A smaller value of n would lead to lessmodulation of signals.

It is noted that n and k of the salt-forming dye are determined bypreparing a test sample in which a dye film is formed on a giventransparent substrate to a thickness equivalent to the recording layerof an optical recording medium, for example, of about 40 to 100 nm underthe same conditions as used for the recording layer, measuring the testsample for reflectance and transmittance in the wavelength region ofrecording light and/or reading light, and calculating n and k from thesemeasurements according to ISHIGURO Kozo, “Optics,” Kyoritsu PublishingK.K., pages 168-178, for example. The reflectance is a reflectance ofthe test sample through the substrate or a reflectance of the samplefrom the dye film side while it is measured in a specular reflectionmode (of the order of 5°). The measurement wavelength is generallyselected herein from the wavelength region of 635 nm, 650 nm and 780 nm.

Formula (I) is first described. In formula (I), A—N═N—B is illustratedas being coordinated although description is herein made on the compoundprior to coordination. A is an aromatic ring group having an activehydrogen-bearing group or a nitrogenous heteroaromatic ring group havingtherein a nitrogen atom coordinatable to a metal ion, and B is anaromatic ring group having an active hydrogen-bearing group.

In the aromatic ring group having an active hydrogen-bearing group,represented by A, the aromatic ring may be either carbocyclic orheterocyclic and either monocyclic or polycyclic as in fused poly-ringsand a ring cluster. Exemplary aromatic rings include benzene,naphthalene, pyridine, thiazole, benzthiazole, oxazole, benzoxazole,quinoline, imidazole, pyrazine, and pyrrole rings, with the benzene ringbeing especially preferred.

The active hydrogen-bearing group is attached to the aromatic ring at aposition adjacent to the diazo group. Examples of the activehydrogen-bearing group include —OH, —SH, —NH₂, —COOH, —CONH₂, —SO₂NH₂,and —SO₃H, with —OH being especially preferred.

In addition to the active hydrogen-bearing group and the azo group, thearomatic ring may further have a substituent, examples of which includenitro groups, halogen atoms (e.g., chlorine and bromine atoms), carboxylgroups, sulfo groups, sulfamoyl groups, and alkyl groups (preferablyhaving 1 to 4 carbon atoms, such as methyl). Of these, nitro groups andhalogen atoms are preferred, with the nitro groups being especiallypreferred. The nitro group is preferably attached at the meta- orpara-position relative to the diazo group. In general, the meta-positionis preferred when the recording/reading light is in the short wavelengthregion of 630 to 690 nm whereas the para-position is preferred when therecording/reading light is in the conventional wavelength region of 770to 830 nm. Two or more substituents may be present, and they may be thesame or different.

In the nitrogenous heteroaromatic ring group having therein a nitrogenatom coordinatable to a metal ion, represented by A, the nitrogenousheteroaromatic ring may be either monocyclic or fused polycyclic.Examples of the nitrogenous heteroaromatic ring include pyridine,thiazole, benzthiazole, oxazole, benzoxazole, quinoline, imidazole,pyrazine, and pyrrole rings, with the pyridine and thiazole rings beingespecially preferred.

The position of the nitrogen atom in the ring is adjacent to the carbonatom to which the azo group is attached.

In addition to the azo group, the nitrogenous heteroaromatic ring mayfurther have a substituent, examples of which include halogen atoms(e.g., chlorine and bromine atoms) and alkyl groups (preferably having 1to 4 carbon atoms, such as methyl).

A is preferably a benzene ring, especially a benzene ring having a nitrogroup as a substituent.

In the aromatic ring group having an active hydrogen-bearing group,represented by B, the aromatic ring is the same as described for A, withthe position of attachment of the active hydrogen-bearing group beingalso the same. Imidazole, benzene, and naphthalene rings are preferredamong others. The benzene and naphthalene rings are more preferred, withthe benzene ring being especially preferred.

The active hydrogen-bearing group is the same as described for A, withits preferred examples being also the same.

In addition to the active hydrogen-bearing group and the azo group, thearomatic ring may further have a substituent, examples of which include

amino groups (which may be unsubstituted amino groups, but arepreferably dialkylamino groups, more preferably dialkylamino groupshaving 2 to 8 carbon atoms in total, for example, dimethylamino,diethylamino, methylethylamino, methylpropylamino, dibutylamino, andhydroxyethylmethylamino groups);

alkoxy groups (in which the alkyl moiety preferably has 1 to 4 carbonatoms, for example, methoxy);

alkyl groups (preferably having 1 to 4 carbon atoms, for example,methyl);

aryl groups (preferably monocyclic, for example, phenyl and o-, m- andp-chlorophenyl groups);

carboxyl groups; and

sulfo groups.

B preferably represents a benzene or naphthalene ring, and especially abenzene ring having a dialkylamino group substituted.

The center metal M₁ is selected from transition metals and other metals,with Co, Mn, Ti, V, Ni, Cu, Zn, Mo, W, Ru, Fe, Pd, Pt, and Al beingpreferred. Among these, V, Mo and W may take the form of an oxide ion,for example, VO²⁺, VO³⁺, MoO₂ ⁺, MoO³⁺, and WO³⁺. Further preferableexamples of the center metals (inclusive of oxide ions) are oxovanadium(VO) such as VO²⁺ and VO³⁺, Co, Ni, and Cu.

Letter m is equal to 1 or 2 while the azo metal complex of formula (I)becomes an anion or cation. Where m is equal to 2, the ligands A—N═N—Bmay be the same or different.

It is noted that in formula (I), the active hydrogen-bearing group inA—N═N—B coordinates to the center metal in the form of an acid anion(—O⁻ where the active hydrogen-bearing group is —OH).

The compound A—N═N—B serving as a ligand is as defined for formula (III)to be described later, and its preferred examples are the same as thecompounds of formulae (IV) and (V)

Next, the ion of cyanine dye of formula (II) which is a counterion tothe ion of azo metal complex of formula (I) is described.

In formula (II), each of Q¹ and Q², which may be the same or different,is a group of atoms forming a 5-membered nitrogenous heterocyclic ringwhich may have a fused ring. Exemplary heterocyclic rings areindolenine, 4,5-benzoindolenine, oxazoline, thiazoline, selenazoline,and imidazoline rings. Preferred examples are indolenine,4,5-benzoindolenine, oxazoline, and thiazoline rings, with theindolenine and 4,5-benzoindolenine rings being especially preferred.Preferred combinations of Q¹ and Q² are a combination of indoleninerings, a combination of 4,5-benzoindolenine rings, and a combination ofan indolenine ring and a 4,5-benzoindolenine ring.

These rings may have substituents, examples of which include halogenatoms, alkyl groups, alkoxy groups, aryl groups, acyl groups, and aminogroups (such as alkylamino groups).

R¹ and R² are alkyl groups. The alkyl groups, which may havesubstituents, are preferably those of 1 to 5 carbon atoms, for example,methyl, ethyl, propyl and butyl groups. Exemplary substituents arehalogen atoms, alkyl groups, aryl groups, ether groups such as alkoxygroups, ester groups, heterocyclic groups, and sulfonato groups. Thealkyl groups represented by R¹ and R² include methyl, ethyl, n-, i-, s-and t-butyl, methoxymethyl, methoxyethyl, ethoxyethyl, sulfonato,methyl, sulfonatoethyl, sulfonatopropyl, and sulfonatobutyl.

L is a methine chain, preferably trimethine or pentamethine, which mayhave a substituent such as methyl. In general, trimethine is preferredwhen the recording/reading light is in the short wavelength region of630 to 690 nm whereas pentamethine is preferred when therecording/reading light is in the conventional wavelength region of 770to 830 nm.

Of the ions of cyanine dyes of formula (II), ions of indolenine,benzothiazoline and benzoxazoline cyanine dyes are preferred, with theions of indolenine cyanine dyes being especially preferred.

Especially preferred are indolenine cyanine dyes of the followingformulae (IIa), (IIb) and (IIc).

In formulae (IIa) to (IIc), R¹, R², and L are as defined in formula(II). R³ is a hydrogen atom or as defined for the substituent in thering completed by Q¹ and Q². Preferred examples of R³ are hydrogenatoms, halogen atoms, alkyl groups and alkoxy groups, with hydrogenatoms, chlorine atoms, methyl groups and methoxy groups being especiallypreferred.

Illustrative, non-limiting, examples of the ions of these cyanine dyesare given below.

Next, the azo oxovanadium metal complex according to the invention isdescribed.

The azo oxovanadium metal complex according to the invention is a metalcomplex of an azo compound of formula (III) with oxovanadium wherein theoxovanadium is present in the form of VO²⁺ or VO³⁺.

Referring to formula (III), A and B in formula (III) have the samemeaning as A and B in formula (I), with their preferred examples beingthe same.

It is understood that the active hydrogen-bearing group in the azocompound of formula (III) coordinates to VO in the form of an acid anion(—O⁻ where the active hydrogen-bearing group is —OH).

The azo oxovanadium metal complexes wherein the counterion is an ion ofa cyanine dye of formula (II), one or two azo compounds of formula (III)coordinate to VO, and k in the wavelength region of recording/readinglight having a short wavelength is up to 0.20 overlap the aforementionedsalt-forming dyes for short wavelength. It is noted that when two azocompounds of formula (III) coordinate to VO, these azo compounds may beidentical or different.

Next, formulae (IV) and (V) are described. In these formulae, X is anactive hydrogen-bearing group, which is the same as that in formula(III), with its preferred examples being the same.

R is a nitro group, and letter n is equal to 0 or 1. When n is 1, thesubstitution position of the nitro group is not critical, but ispreferably the meta-position relative to the nitro group preexisting informula (IV) or (V).

R¹ and R² are alkyl groups, which are usually the same, but may bedifferent. The total number of carbon atoms in R¹ and R² is 2 to 8. Thenumber of carbon atoms in such an alkyl group is preferably 1 to 4.Exemplary alkyl groups are methyl, ethyl, n- and i-propyl, and n-, i-,s- and t-butyl groups. These alkyl groups may have a substituent such asa hydroxyl group, and exemplary substituted alkyl groups arehydroxylmethyl and hydroxyethyl.

The azo metal complex of the invention is obtained by reacting at leastone of azo compounds of formulae (IV) and (V) with a metal compound. Thecenter metal is preferably selected from Co, Mn, Ti, V, Ni, Cu, Zn, Mo,W, Ru, Fe, Pd, Pt, and Al. Among these, V, Mo and W may take the form ofan oxide ion, for example, VO²⁺, VO³⁺, MoO₂ ⁺, MoO³⁺, and WO³⁺. Furtherpreferable examples of the center metal are oxovanadium (VO) such asVO²⁺ and VO³⁺, Co, Ni, and Cu.

Of the compounds of formulae (IV) and (V), azo compounds of formula (V)are especially preferred because the invention aims at recording andreading in the short wavelength region of 630 to 690 nm.

The oxovanadium complexes obtained from the azo compounds of formulae(IV) and (V) are encompassed within the oxovanadium complexes obtainedfrom the azo compounds of formula (III), with the former being preferredones among the latter complexes.

The azo metal complexes wherein the center metal is a transition metal,one or two azo compounds of formula (IV) or (V) coordinate thereto, thecounterion is a cation of a cyanine dye of formula (II), and k in thewavelength region of recording/reading light having a short wavelengthis up to 0.20 overlap the aforementioned salt-forming dyes.

In the azo metal complexes of the azo compounds of formulae (IV) and(V), when the ligand of the azo compound and the center metal are in aratio of 2:1, two types of azo compounds may coordinate as the ligands.

The above azo oxovanadium metal complexes and azo metal complexessometimes have an electric charge depending on the valence of the centermetal, and in such a case, a counter-ion is present. Examples of thecounterion is an inorganic cation such as Na⁺, Li⁺ and K⁺, R¹R²R³R⁴N⁺wherein R¹, R², R³ and R⁴ each are a hydrogen atom, alkyl group oralkoxy group, and R¹R²R³N⁺—(CH₂)_(k)—N⁺R³R²R¹ wherein R¹, R², R³ and R⁴each are a hydrogen atom, alkyl group or alkoxy group, and k is 5 to 10.Of these, R¹R²R³N⁺—(CH₂)_(k)—N⁺R³R²R¹ are preferred from the standpointsof solubility and medium characteristics. The ions of trimethine cyaninedyes described in conjunction with the above salt-forming dyes are alsopreferred, of which trimethine indolenine cyanine dye cations areespecially preferred.

Illustrative examples of the azo metal complex compounds which can beused herein are given below. They are shown by combinations of an azocompound, a center metal M₁, and a counterion while the azo compoundsare shown by combinations of A and B in formula (III). Where thecounterion is an ion of a cyanine dye, examples are shown bycombinations of A, B, M₁, m and counterion in accordance with formula(I).

It is noted that Me, Et, Pr, and Bu in A and B stand for methyl, ethyl,propyl and butyl, respectively.

A—N═N—B (III) Compound A B M₁ Counterion 1

VO

2

Co

3

VO

4

VO

5

VO

6

VO

7

VO

8

VO

9

VO

10

VO

11

VO

12

VO

13

VO

14

VO

15

VO

16

VO

17

VO

18

VO

19

Ni

20

Mn

21

VO

22

Co

23

VO

24

Cu

(A—N═N—B)_(m).M₁ (I) Compound A B M₁ Counterion m C-1

VO B-8 2 C-2

VO B-9 2 (a ligand wherein C-3

VO B-3 2 (a ligand wherein

1:1 mixed ligand C-4

VO B-8 2 (a ligand wherein

1:1 mixed ligand C-5

VO B-8 2 C-6

Co B-8 2 C-7

Ni B-8 2 C-8

VO B-9 2 C-9

Co B-9 2 C-10

Ni B-9 2 C-11

VO B-11 2 C-12

VO B-12 2 C-13

Co B-13 2 C-14

Ni B-15 2 C-15

VO B-13 2 C-16

VO B-11 2 C-17

Co B-11 2 C-18

Ni B-12 2 C-19

VO B-8 2 C-20

VO B-8 2 C-21

Co B-8 2 C-22

Ni B-8 2 C-23

Cu B-8 2 C-24

VO B-9 2 C-25

Co B-19 2 C-26

Co B-15 1 C-27

Co B-8 2 C-28

VO B-8 2 C-29

Co B-21 2 (a ligand wherein

1:1 mixed ligand C-30

VO B-26 2 C-31

Co B-28 2 C-32

Co B-18 2 D-1

VO B-39 2 D-2

Co B-48 2 D-3

VO B-42 2 D-4

Co B-32 2 D-5

Co B-32 2 D-6

Co B-32 2 D-7

Co B-32 2 D-8

Ni B-50 2 D-9

VO B-50 2 D-10

Co B-35 2 D-11

Co B-41 2 D-12

Co B-41 2 D-13

Co B-41 2 D-14

Co B-41 2 D-15

Co B-45 1 D-16

Co B-45 1 D-17

Co B-51 1 D-18

Co B-51 1 D-19

Co B-51 1 D-20

Co B-51 1 D-21

Cu B-32 2 D-22

Co B-49 2

The azo compounds used herein can be synthesized in accordance with thedisclosure of Furukawa, Anal. Chim. Acta., 140, 289 (1982), for example.

The compounds can be identified by a mass spectrum, ¹H-nuclear magneticresonance spectrum, infrared absorption spectrum, elemental analysis,etc.

Further, the azo metal complex compounds can be obtained by reacting azocompounds as mentioned above with metal compounds in aqueous solventssuch as water-alcohol solvents. The metal compounds which are generallyused herein include chlorides (for example, cobalt chloride, zincchloride, chromium chloride, manganese chloride, iron chloride, andvanadium oxytrichloride) and complex compounds (for example, vanadiumacetylacetone). Complex forming reaction may be carried out at atemperature of about 90° C. for about 10 hours whereupon crystals aregenerally obtained. If necessary to provide the desired counterion(e.g., cyanine dye ion), salt exchange is carried out.

The resulting compound can be identified by elemental analysis,visible/ultraviolet absorption spectroscopy, fluorescent x-ray analysis,etc.

Synthesis examples are shown below.

Synthesis Example 1

Synthesis of Compound 1

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 1.37 g (10 mmol) ofN,N-dimethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) ofsodium hydroxide for effecting coupling reaction. After the completionof reaction, crystals were collected by suction filtration and thendried in vacuum, obtaining a ligand.

To 0.606 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.67 g of a complex.

This complex, 0.67 g (1 mmol), was dissolved in 6.7 g of DMF, with which0.14 g (3 mmol) of formic acid and 0.086 g (0.5 mmol) ofN,N,N′,N′-tetramethyl-1,6-diaminohexane were mixed. The mixture wassubject to reaction at 70° C. for 2 hours. After the completion ofreaction, water was added for precipitation. Crystals were collected bysuction filtration and then dried in vacuum, obtaining 0.67 g of acomplex.

Synthesis Example 2

Synthesis of Compound 2

To 0.606 g (2 mmol) of the ligand obtained in Synthesis Example 1 wereadded 0.012 g of sodium hydroxide, 10 g of water and 20 g of ethanol.With 0.129 g (1 mmol) of cobalt (II) chloride added, the mixture wassubject to reaction at 95° C. for 16 hours. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining 0.60 g of a complex. Thereafter, the end compoundwas obtained as in Synthesis Example 1.

Synthesis Example 3

Synthesis of Compound 3

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 1.65 g (10 mmol) ofN,N-diethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) of sodiumhydroxide for effecting coupling reaction. After the completion ofreaction , crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.662 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.65 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

Synthesis Example 4

Synthesis of Compound 4

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 2.21 g (10 mmol) ofN,N-dibutyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) of sodiumhydroxide for effecting coupling reaction. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.774 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.65 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

Synthesis Example 5

Synthesis of Compound 5

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-5-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 2.21 g (10 mmol) ofN,N-dibutyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) of sodiumhydroxide for effecting coupling reaction. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.774 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.65 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

Synthesis Example 6

Synthesis of Compound 6

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 1.24 g (10 mmol) of3-methoxyphenol in 20 g of water and 2.0 g (50 mmol) of sodium hydroxidefor effecting coupling reaction. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining a ligand.

To 0.580 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.65 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

Synthesis Example 7

Synthesis of Compound 7

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-5-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thediazonium salt was slowly added to a solution of 1.65 g (10 mmol) ofN,N-diethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) of sodiumhydroxide for effecting coupling reaction. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.662 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.65 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

Synthesis Example 8

Synthesis of Compound 21

In 2 ml of water and 20 ml of ethanol was dissolved 1.99 g (10 mmol) of2-amino-4,6-dinitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol)of sodium nitrite in 15 ml of water was slowly added for diazotation.The diazonium salt was slowly added to a solution of 1.37 g (10 mmol) ofN,N-dimethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) ofsodium hydroxide for effecting coupling reaction. After the completionof reaction, crystals were collected by suction filtration and thendried in vacuum, obtaining a ligand.

To 0.696 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.80 g of a complex. Thereafter, the end compound was obtainedas in Synthesis Example 1.

This complex, 0.76 g (1 mmol), was dissolved in 8.0 g of DMF, with which0.14 g (3 mmol) of formic acid and 0.086 g (0.5 mmol) ofN,N,N′,N′-tetramethyl-1,6-diaminohexane were mixed. The mixture wassubject to reaction at 70° C. for 2 hours. After the completion ofreaction, water was added for precipitation. Crystals were collected bysuction filtration and then dried in vacuum, obtaining 0.73 g of acomplex.

Synthesis Example 9

Synthesis of Compound C-5

A solution of 0.67 g (1 mmol) of Compound 1 in 6.7 g of DMF was mixedwith 0.58 g (1 mmol) of a ClO₄ salt of Compound B-9, and reaction waseffected at 70° C. for 2 hours. After the completion of reaction, waterwas added for precipitation. Crystals were collected by suctionfiltration and then dried in vacuum, obtaining 0.88 g of a complex.

Synthesis Example 10

Synthesis of Compound C-6

A solution of 0.68 g (1 mmol) of Compound 2 in 6.7 g of DMF was mixedwith 0.58 g (1 mmol) of a ClO₄ salt of Compound B-9, and reaction waseffected at 70° C. for 2 hours. After the completion of reaction, waterwas added for precipitation. Crystals were collected by suctionfiltration and then dried in vacuum, obtaining 0.90 g of a complex.

Synthesis Example 11

Synthesis of Compound C-24

In 2 ml of water and 20 ml of ethanol was dissolved 2.31 g (15 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 1.09 g of sodiumnitrite in 15 ml of water was slowly added for diazotation. Then asolution of 2.39 g (15 mmol) of 8-amino-2-naphthol in 30 g of ethanoland an aqueous solution of 20% sodium hydroxide were added dropwise tothe solution so as to control its pH at 7 to 9. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.648 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.58 g of a complex (Metal Complex A).

Equimolar amounts of this complex and a ClO₄ salt of Compound B-9 weredissolved in DMF, and reaction was effected at 70° C. for 2 hours. Afterthe completion of reaction, water was added for precipitation. Crystalswere collected by suction filtration and then dried in vacuum, obtainingthe end compound.

Synthesis Example 12

Synthesis of Compound C-25

To 0.648 g (2 mmol) of the ligand obtained in Synthesis Example 11 wereadded 0.012 g of sodium hydroxide, 10 g of water and 20 g of ethanol.With 0.129 g (1 mmol) of cobalt (II) chloride added, the mixture wassubject to reaction at 95° C. for 16 hours. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining 0.52 g of a complex.

Equimolar amounts of this complex and a ClO₄ salt of Compound B-19 weredissolved in DMF, and reaction was effected at 70° C. for 2 hours. Afterthe completion of reaction, water was added for precipitation. Crystalswere collected by suction filtration and then dried in vacuum, obtainingthe end compound.

Synthesis Example 13

Synthesis of Compound C-26

In 2 ml of water and 20 ml of ethanol was dissolved 1.39 g (10 mmol) of2-amino-4-nitropyridine. With stirring at 0 to 5° C., 0.69 g (10 mmol)of sodium nitrite in 15 ml of water was slowly added for diazotation.Then the diazonium salt was slowly added to a solution of 1.37 g (10mmol) of N,N-dimethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol)of sodium hydroxide for effecting coupling reaction. After thecompletion of reaction, crystals were collected by suction filtrationand then dried in vacuum, obtaining a ligand.

To 0.574 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.129 g (1mmol) of cobalt (II) chloride added, the mixture was subject to reactionat 95° C. for 16 hours. After the completion of reaction, crystals werecollected by suction filtration and then dried in vacuum, obtaining 0.60g of a complex.

Equimolar amounts of this complex and a Na salt of Compound B-15 weredissolved in methanol, and the mixture was refluxed for 2 hours. Afterthe completion of reaction, ice bag cooling caused precipitation ofcrystals which were collected by suction filtration. The crystals weredried in vacuum, obtaining the end compound.

Synthesis Example 14

Synthesis of Compound D-1

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thenthe diazonium salt was slowly added to a solution of 1.37 g (10 mmol) ofN,N-dimethyl-m-aminophenol in 20 g of water and 2.0 g (50 mmol) ofsodium hydroxide for effecting coupling reaction. After the completionof reaction, crystals were collected by suction filtration and thendried in vacuum, obtaining a ligand.

To 0.606 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.67 g of a complex (Metal Complex B).

Equimolar amounts of this complex and a ClO₄ salt of Compound B-39 weredissolved in DMF, and reaction was effected at 70° C. for 2 hours. Afterthe completion of reaction, water was added for precipitation. Crystalswere collected by suction filtration and then dried in vacuum, obtainingthe end compound.

Synthesis Example 15

Synthesis of Compound D-2

To 0.606 g (2 mmol) of the ligand obtained in Synthesis Example 14 wereadded 0.012 g of sodium hydroxide, 10 g of water and 20 g of ethanol.With 0.129 g (1 mmol) of cobalt (II) chloride added, the mixture wassubject to reaction at 95° C. for 16 hours. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining 0.60 g of a complex.

Equimolar amounts of this complex and a BF₄ salt of Compound B-49 weredissolved in DMF, and reaction was effected at 70° C. for 2 hours. Afterthe completion of reaction, water was added for precipitation. Crystalswere collected by suction filtration and then dried in vacuum, obtainingthe end compound.

Synthesis Example 16

Synthesis of Compound D-3

In 2 ml of water and 20 ml of ethanol was dissolved 1.54 g (10 mmol) of2-amino-4-nitrophenol. With stirring at 0 to 5° C., 0.69 g (10 mmol) ofsodium nitrite in 15 ml of water was slowly added for diazotation. Thena solution of 1.44 g (10 mmol) of 2-naphthol in 20 g of ethanol and anaqueous solution of 20% sodium hydroxide were added dropwise to thesolution so as to control its pH at 7 to 9. After the completion ofreaction, crystals were collected by suction filtration and then driedin vacuum, obtaining a ligand.

To 0.544 g (2 mmol) of the thus synthesized ligand were added 0.012 g ofsodium hydroxide, 10 g of water and 20 g of ethanol. With 0.265 g (1mmol) of vanadium acetylacetone added, the mixture was subject toreaction at 95° C. for 16 hours. After the completion of reaction,crystals were collected by suction filtration and then dried in vacuum,obtaining 0.55 g of a complex.

Equimolar amounts of this complex and a PF₆ salt of Compound B-42 weredissolved in DMF, and reaction was effected at 70° C. for 2 hours. Afterthe completion of reaction, water was added for precipitation. Crystalswere collected by suction filtration and then dried in vacuum, obtainingthe end compound.

Other exemplified compounds can be synthesized as above.

The azo metal complex compounds according to the invention have amelting point (mp) of 100 to 300° C. and a λmax (as measured on a dyethin film of 50 nm thick) in the range of 590 to 625 nm for the shortwavelength application and in the range of 600 to 700 nm for the longwavelength application.

Of these dyes, those dyes for the short wavelength application have acomplex index of refraction at 635 nm or 650 nm whose real part n is2.10 to 2.7 and whose imaginary part k is up to 0.20, preferably 0.02 to0.10. On the other hand, those dyes for the long wavelength applicationhave a complex index of refraction at 780 nm whose real part n is 2.0 to2.6 and whose imaginary part k is up to 0.20, preferably 0.02 to 0.10.Understandably, n and k are determined as previously described.

For the above-illustrated compounds, their λmax, n and k are shownbelow. For the compounds having a cyanine dye ion as the counterion, allthe exemplified compounds are shown. For the other compounds, those usedin examples of the two wavelength accommodating type are shown.

TABLE 1 n k Compound (650 nm) λmax/nm 1 2.35 0.02 618 2 2.40 0.03 620 32.25 0.03 625 5 2.25 0.03 620 7 2.35 0.03 625 8 2.50 0.03 628 19  2.300.02 610 20  2.35 0.02 615

TABLE 2 n k Compound (650 nm) λmax/nm C-1  2.50 0.12 630 C-2  2.50 0.10631 C-3  2.40 0.02 622 C-4  2.30 0.05 620 C-5  2.35 0.04 618 C-6  2.400.02 620 C-7  2.35 0.02 615 C-8  2.40 0.08 625 C-9  2.45 0.12 630 C-102.40 0.07 628 C-11 2.45 0.08 626 C-12 2.40 0.07 625 C-13 2.50 0.03 620C-14 2.40 0.02 618 C-15 2.45 0.03 622 C-16 2.40 0.05 623 C-17 2.45 0.07622 C-18 2.35 0.04 625 C-19 2.35 0.02 618 C-20 2.35 0.02 619 C-21 2.400.05 623 C-22 2.35 0.04 621 C-23 2.40 0.06 625 C-24 2.40 0.10 629 C-252.40 0.13 630 C-26 2.30 0.08 628 C-27 2.40 0.08 627 C-28 2.35 0.04 620C-29 2.40 0.07 625 C-30 2.35 0.04 621 C-31 2.30 0.02 618 C-32 2.30 0.15632

TABLE 3 n k Compound (650 nm) λmax/nm D-1  2.35 0.02 705 D-2  2.25 0.03700 D-3  2.45 0.04 715 D-4  2.45 0.07 725 D-5  2.45 0.07 723 D-6  2.400.07 724 D-7  2.40 0.07 724 D-8  2.20 0.03 703 D-9  2.15 0.02 700 D-102.20 0.05 710 D-11 2.35 0.10 730 D-12 2.45 0.13 735 D-13 2.35 0.07 715D-14 2.35 0.07 713 D-15 2.35 0.08 715 D-16 2.35 0.07 718 D-17 2.25 0.07717 D-18 2.45 0.08 715 D-19 2.30 0.05 710 D-20 2.35 0.05 711 D-21 2.450.08 715 D-22 2.20 0.02 701

The azo metal complexes of the invention which can be used as the dyefor the recording layer may be used alone or in admixture of two ormore.

These compounds are highly resistant to light and fully soluble inorganic solvents, that is, have a high solubility in coating solventswhich do not attack polycarbonate (PC) resins commonly used as thesubstrate material for optical recording media.

Recording layers using these compounds are especially preferred for usein write-once type optical recording discs (CD-R) and digital videodiscs (DVD-R) whereby recording and reading at the conventionalwavelength or a short wavelength becomes possible depending on theoptical characteristics of a particular compound. The recording layer ispreferably formed using a coating solution containing a dye. Especiallypreferred is a spin coating technique of applying and spreading acoating solution onto a rotating substrate. Alternatively, gravurecoating, spray coating and dipping may be used. Note that the coatingsolvent used herein will be described later.

After spin coating as mentioned above has been completed, the coating isdried, if required. The thus formed recording layer has usually athickness of 500 to 3,000 Å although it may be appropriately determineddepending on the desired reflectance, etc.

It is understood that the dye content of the coating solution ispreferably 0.05 to 10% by weight. Since the azo metal complex dye of theinvention is well soluble, a coating solution of such concentration canbe readily prepared. More illustratively, the azo metal complex dyesaccording to the invention show a high solubility mainly in polarsolvents, for example, a solubility of 0.5 to 10% by weight in alcoholsand cellosolve or alkoxyalcohol solvents, ketoalcohols such as diacetonealcohol, ketones such as cyclohexanone, and fluorinated alcohols such as2,2,3,3-tetrafluoropropanol. In particular, the dyes are soluble inethyl cellosolve and 2,2,3,3-tetrafluoropropanol, which are appropriatecoating solvents in coating on polycarbonate disc substrates, in aconcentration of more than 4% by weight, enabling brief formation of aspin coated film of quality.

The coating solution may optionally contain binders, dispersants, andstabilizers.

In addition to the azo metal complex, the recording layer of the opticalrecording medium according to the invention may contain a lightabsorbing dye of another type. Examples of the other dye includephthalocyanine dyes, cyanine dyes, metal complex dyes of a type otherthen the aforementioned, styryl dyes, porphyrin dyes, azo dyes of a typeother than the aforementioned, and formazane metal complexes.

In such embodiments, such a dye may be contained in the coatingsolution, from which a recording layer is formed.

Of the above-described azo metal complex compounds, the salt-formingdyes having a pentamethine cyanine dye ion as the counterion (compoundsfor the long wavelength application) are preferably used, due to theiroptical characteristics, in CD-R of carrying out recording and readingat a wavelength of about 770 to 830 nm, especially about 780 nm.

The salt-forming dyes having a trimethine cyanine dye ion as thecounterion, the azo oxovanadium metal complexes, and the azo metalcomplexes having compounds of formulae (IV) and (V) as the ligand(compounds for the short wavelength application) are preferably used,due to their optical characteristics, in DVD-R of carrying out recordingand reading at a wavelength of about 690 to 630 nm, especially about 635to 680 nm.

Also the compounds for the short wavelength application are appropriatefor use in optical recording media which can be recorded and read at twowavelengths, a short wavelength of about 630 to 690 nm, especially about635 to 680 nm and a conventional wavelength of about 770 to 830 nm,especially about 780 nm or optical recording media which can be recordedat either of the two wavelengths and read at the other wavelength. Inthis embodiment, the inventive medium is suitable for use in therecording and reading mode of CD-RII involving recording at theconventional wavelength of about 780 nm and reading at two wavelengths,a short wavelength and the conventional wavelength of about 780 nm. Forsuch application, the recording layer should preferably contain, incombination, an azo metal complex compound for the short wavelengthapplication according to the invent on and a dye having differentoptical characteristics (such as absorption characteristics), typicallydifferent optical constants. A dye having an absorption maximum (λmax)at about 680 to 750 nm is preferably contained in addition to the azometal complex for the short wavelength application according to theinvention. The dye having such an absorption maximum (λmax) may beselected from the above-mentioned dyes. Among others, a choice isgenerally made of phthalocyanine dyes and pentamethinecyanine dyes. Thecompounds for the long wavelength application according to the inventionmay also be used.

Especially for use in a recording layer of the CD-RII mode involvingrecording and reading at two wavelengths as mentioned above, the azometal complex should preferably have a complex index of refraction at650 nm whose real part n is 1.8 to 2.6 and imaginary part k is 0.02 to0.20. The other dye to be combined therewith should preferable have acomplex index of refraction at 780 nm whose real part n is 1.8 to 2.6and imaginary part k is 0.02 to 0.30, especially 0.02 to 0.15 for use ina recording layer of the laminate layer type. For the other dye, thehalf band width of the absorption spectrum of a thin film thereof, thatis, the half band width of a spectral line near λmax is preferably up to170 nm, more preferably up to 150 nm. The lower limit of the half bandwidth is generally 50 nm though not critical. The use of a dye havingsuch a half band width eliminates any influence on the absorptioncharacteristics of the azo metal complex used in combination so that asatisfactory reflectance and modulation in a short wavelength region areavailable. In contrast, if the half band width exceeds 170 nm, theabsorption edge overlaps the wavelength region of a short wavelengthlaser, causing a loss of reflectance in the short wavelength region. Itis noted that the half band width is determined by preparing a sample inwhich a dye film is formed on a transparent substrate such that thetransmittance T at absorption maximum λmax is up to 25%, and measuringan absorption spectrum of the sample. Referring to the absorptionspectrum of FIG. 1, for example, a transmittance T at λmax and atransmittance T₂ which is substantially constant when the wavelength isshifted toward a longer wavelength side, that is, does not depend on ashift of wavelength are determined. The width αλ at one-half of thebottom depth measured from T₂ as a base to T₁ is the half band width.The dye film as the sample is generally about 50 to 150 nm thick.

It is noted that the above-mentioned values of n and k are determined inthis way while setting the measurement wavelength at 650 nm and 780 nm.

Among such dyes, phthalocyanine dyes of formula (VI) are especiallypreferred.

Formula (VI) is described. In formula (VI), M is a center atom. Includedin the center atom represented by M are a hydrogen atom (2H) or a metalatom. Examples of the metal atom used herein are those in Groups 1 to 14of the Periodic Table (Groups 1A to 7A, 8, and 1B to 4B). For example,mention is made of Li, Na, K, Mg, Ca, Ba, Ti, Zr, V, Nb, Ta, Cr, Mo, W,Mn, Tc, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt, Cu, Ag, Au, Zn, Cd, Hg, Al,In, Tl, Si, Ge, Sn and Pb, more specifically, Li, Na, K, Mg, Ca, Ba, Ti,Zr, V, Nb, Ta, Cr, Mo, W, Mn, Tc, Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt,Cu, Ag, Au, Cd, Hg, Al, In, Tl, Si, Ge, Sn, and Pb. Preferred amongthese are Al, Si, Ge, Sn, Cu, Pd, Ni, Fe, and Co, especially Cu, Pd, Ni,Fe, Co, and VO for aging stability.

It is understood that these metal atoms may take a form having oxygencoordinated thereto like V taking the form of VO. Alternatively, themetal atom may further have a ligand or ligands such as ether groups,ester groups, pyridine and derivatives thereof coordinated to the upperand/or lower sides or one lateral side, as in the case of Si, Al, Ge,Co, and Fe.

Each of X₁ to X₄ is a halogen atom, for example, F, Cl, Br, and I. Brand F are especially preferred.

Each of p1, p2, p3, and p4 is 0 or an integer of 1 to 4, and the sum ofp1+p2+p3+p4 is 0 to 15, preferably 0 to 10.

X₁ to X₄ may be the same or different. Where each of p1, p2, p3, and p4is an integer of 2 or more, X₁ groups, X₂ groups, X₃ groups or X₄ groupsmay be the same or different, respectively.

Each of Y₁ to Y₄ is an oxygen or sulfur atom, with the oxygen atom beingespecially preferred. Y₁ to Y₄ are generally the same though they may bedifferent.

Each of Z₁ to Z₄ is an alkyl group, alicyclic hydrocarbon group,aromatic hydrocarbon group or heterocyclic group each having at least 4carbon atoms, and they may be the same or different.

Each of q1, q2, q3, and q4 is 0 or an integer of 1 to 4, they are notequal to 0 at the same time, and the sum of q1+q2+q3+q4 is 1 to 8,preferably 2 to 6.

The position at which Y₁ to Y₄ are attached to the phthalocyanine ringis preferably the 3- and/or 6-position of the phthalocyanine ring (asseen from the structural formula shown below), and the inclusion of atleast one such bond is preferred.

The alkyl groups represented by Z₁ to Z₄ are preferably those having 4to 16 carbon atoms. These alkyl groups may be either normal or branchedalthough the branched ones are preferred. The alkyl groups may have asubstituent which is a halogen atom (such as F, Cl, Br, and I,especially F and Br), etc. Examples of the alkyl group include n-C₄H₉—,i-C₄H₉—, s-C₄H₉—, t-C₄H₉—, n-C₅H₁₁—, (CH₃)₂CHCH₂CH₂—, (CH₃)₃CCH₃—,(C₂H₅)₂CH—, C₂H₅C(CH₃)₂—, n-C₃H₇CH(CH₃)—, n-C₆H₁₃—, (CH₃)₂CHCH₂CH₂CH₂—,(CH₃)₃C—CH₂—CH₂—, n-C₃H₇CH(CH₃)CH₂—, n-C₄H₉CH(CH₃)—, n-C₇H₁₅—,[(CH₃)₂CH]₂—CH—, n-C₄H₉CH(CH₃)CH₂—, (CH₃)₂CHCH₂CH(CH₃)CH₂—, n-C₈H₁₇—,(CH₃)₃CCH₂CH(CH₃)CH₂—, (CH₃)₂CHCH (i-C₄H₉)—, n-C₄H₉CH(C₂H₅)CH₂—,n-C₉H₁₉—, CH₃CH₂CH(CH₃)CH₂CH(CH₃)CH₂CH₂—, (CH₃)₂CHCH₂CH₂CH₂CH(CH₃)CH₂—,n-C₃H₇CH(CH₃)CH₂CH(CH₃)CH₂—, n-C₁₀H₂₁—, (CH₃)₃CCH₂CH₂C(CH₃)₂CH₂—,n-C₁₁H₂₃—, n-C₁₂H₂₅—, n-C₁₃H₂₇—, n-C₁₄H₂₉—, n-C₁₅H₃₁—, n-C₁₆H₃₃—,n-C₄F₉—, i-C₄F₉—, s-C₄F₉—, and t-C₄F₉—.

The alicyclic hydrocarbon groups represented by Z₁ to Z₄ includecyclohexyl, cyclopentyl and other groups, with the cyclohexyl groupbeing preferred. These groups may have a substituent which includes analkyl group, aryl group, alkoxy group, aryloxy group, aralkyl group,halogen atom, nitro group, carboxyl group, ester group, acyl group,amino group, amide group, carbamoyl group, sulfonyl group, sulfamoylgroup, sulfo group, sulfino group, arylazo group, alkylthio group, andarylthio group. Preferred substituents are alkyl groups having 1 to 5carbon atoms (e .g., methyl, ethyl, n-propyl, iso-propyl, n-butyl,iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-pentyl, neo-pentyl,tert-pentyl, and 1-methylbutyl groups), alkoxy groups (e.g., methoxy,ethoxy, propoxy, isopropoxy, butoxy, isobutoxy, sec-butoxy, andtert-butoxy groups), aryl groups (e.g., phenyl, tolyl, biphenyl andnaphthyl groups), and halogen atoms (e.g., F, Cl, Br, and I, with F andBr being preferred). The replacement position of these substituents ispreferably either one or both of the positions adjacent to the positionof attachment to each of Y₁ to Y₄. The inclusion of at least one suchsubstitution is preferred.

The aromatic hydrocarbon groups represented by Z_(1 to Z) ₄ may bemonocyclic or have a fused ring and may have a substituent. The totalnumber of carbon atoms is preferably 6 to 20. Examples are phenyl andnaphthyl groups, with the phenyl group being preferred. They may have asubstituent while examples and preferred examples of the substituent arethe same as exemplified for the alicyclic hydrocarbon groups. Thereplacement position is also the same as previous, preferablyortho-position to the position of attachment to each of Y₁ to Y₄. Theinclusion of at least one ortho-substitution is preferred.

The heterocyclic groups represented by Z₁ to Z₄ may be monocyclic orhave a fused ring while the preferred hetero-atom is oxygen, nitrogen,sulfur, etc., with oxygen and nitrogen being especially preferred.Exemplary groups include pyridyl, furanonyl, pyrazyl, pyrazolidyl,piperidinonyl, quinoxalyl, pyranonyl and thiophenetrionyl groups, withthe pyridyl and 2-furanonyl groups being preferred. These heterocyclicgroups may further have a substituent while examples and preferredexamples of the substituent are the same as exemplified for thealicyclic hydrocarbon and aromatic hydrocarbon groups. Where there is acarbon atom adjacent to the position of attachment to each of Y₁ to Y₄,it is preferred to have a substituent at such an adjacent position.

Preferred for Z₁ to Z₄ are alicyclic hydrocarbon and aromatichydrocarbon groups, with cyclohexyl and phenyl groups being especiallypreferred, while it is preferred to have a substituent (especially thepreferred substituents mentioned above) at one or both of the positionsadjacent to the position of attachment to each of Y₁ to Y₄.

Illustrative examples of these phthalocyanine dyes are shown belowalthough the invention is not limited thereto. These illustrativeexamples are shown in terms of X₁₁ to X₁₄, X₁₅ to X₁₈, X₁₉ to X₂₂, X₂₃to X₂₆ and M in the following formula (VI-1). Where all of X₁₁ to X₁₄etc. are hydrogen, it is shown by “H.” Where any of X₁₁ to X₁₄ has asubstituent, only the substituted one is shown, with the expression “H”being omitted. It is understood that the 3 and 6-positions and the 4 and5-positions of the phthalocyanine ring are equivalent to each other andwhere a substituent is present at either one of these positions, onlyone is shown as a representative example.

Dye No. X₁₁˜X₁₄ X₁₅˜X₁₈ X₁₉˜X₂₂ X₂₃˜X₂₆ M A-1

Cu A-2

Pd A-3

Cu A-4

Cu A-5

Cu A-6

Cu A-7

Cu A-8

Cu A-9

Cu A-10

Cu A-11

Cu A-12

Cu A-13

Cu X₁₂ = X₁₃ = X₁₄ = Br X₁₆ = X₁₇ = X₁₈ = Br X₂₀ = X₂₁ = X₂₂ = Br X₂₄ =X₂₅ = X₂₆ = Br A-14

Cu X₁₂ = X₁₃ = F X₁₆ = X₁₇ = F X₂₀ = X₂₁ = F X₂₄ = X₂₅ = F A-15

H

H Cu A-16

H

Cu A-17

H

H Cu A-18

Cu A-19

Pd A-20

Ni A-21

Fe A-22

Co A-23

VO A-24

Cu A-25

Cu A-26

Cu A-27

Cu A-28

Cu A-29

Cu A-30

Cu A-31

Cu A-32

Cu A-33

Cu X₁₂ = X₁₃ = X₁₄ = Br X₁₆ = X₁₇ = X₁₈ = Br X₂₀ = X₂₁ = X₂₂ = Br X₂₄ =X₂₅ = X₂₆ = Br A-34

Cu X₁₂ = X₁₃ = F X₁₆ = X₁₇ = F X₂₀ = X₂₁ = F X₂₄ = X₂₅ = F A-35

H

H Cu A-36

H

Cu A-37

H

H Cu A-38

Cu A-39

Pd A-40

Ni A-41

Fe A-42

Co A-43

VO A-44

Cu A-45

Cu A-46

Cu A-47

Cu A-48

Cu A-49

Ni A-50

Cu A-51

Co

The aforementioned phthalocyanine dyes may be synthesized in the lightof methods as disclosed in JP-A 313760/1988, JP-A 301261/1988, EP675489, etc.

These dyes have a melting point (mp) of 60 to 400° C.

These phthalocyanine dyes have n and k at 780 nm as reported in Tables 4and 5. These values of n and k were determined using a dye film of 80 nmthick. The half band width of an absorption spectrum of a dye thin filmwas also determined as mentioned above, with the results being reportedtogether with λmax (thin film).

TABLE 4 Half band Dye n k λmax, nm width, nm No. (780 nm) (absorptionspectrum) A-1  2.2 0.08 724 130 A-2  2.3 0.05 715 140 A-3  2.4 0.10 725125 A-4  2.3 0.10 724 130 A-5  2.3 0.11 724 125 A-6  2.4 0.10 725 130A-7  2.3 0.09 723 120 A-8  2.2 0.10 725 140 A-9  2.2 0.10 723 120 A-102.3 0.11 723 130 A-11 2.2 0.11 723 125 A-12 2.1 0.10 726 125 A-13 2.20.10 727 125 A-14 2.2 0.10 725 125 A-15 2.2 0.11 723 130 A-16 2.3 0.12725 130 A-17 2.3 0.10 723 125 A-18 2.3 0.09 725 125 A-19 2.2 0.05 715130 A-20 2.2 0.08 720 130 A-21 2.2 0.07 718 135 A-22 2.2 0.08 720 140A-23 2.2 0.13 730 120 A-24 2.2 0.11 725 125 A-25 2.2 0.10 726 125

TABLE 5 Half band Dye n k λmax, nm width, nm No. (780 nm) (absorptionspectrum) A-26 2.3 0.09 725 130 A-27 2.3 0.09 720 135 A-28 2.4 0.09 725130 A-29 2.3 0.10 720 125 A-30 2.4 0.11 723 125 A-31 2.3 0.10 721 125A-32 2.2 0.11 722 130 A-33 2.3 0.10 724 125 A-34 2.4 0.10 725 130 A-352.4 0.10 721 125 A-36 2.4 0.10 722 135 A-37 2.3 0.09 725 140 A-38 2.30.09 725 135 A-39 2.3 0.07 715 135 A-40 2.3 0.08 720 135 A-41 2.3 0.08720 125 A-42 2.3 0.08 720 135 A-43 2.2 0.09 728 140 A-44 2.2 0.09 728140 A-45 2.2 0.09 726 135 A-46 2.2 0.10 727 140 A-47 2.2 0.09 723 130A-48 2.2 0.10 725 135 A-49 2.3 0.08 718 140 A-50 2.2 0.10 726 125 A-512.1 0.07 718 130

It is noted that these dyes may be used alone or in admixture of two ormore.

The coating solvent used in the practice of the invention may beselected from alcohol solvents (including keto-alcohols andalkoxyalcohols such as ethylene glycol monoalkyl ethers), aliphatichydrocarbon solvents, ketone solvents, ester solvents, ether solvents,aromatic solvents, halogenated alkyl solvents, etc.

Preferred among these are alcohol and aliphatic hydrocarbon solvents.Preferable alcohol solvents are alkoxy-alcohols and keto-alcohols. Inthe preferred alkoxy-alcohols, the alkoxy moiety has 1 to 4 carbonatoms, the alcohol moiety has 1 to 5 carbon atoms, especially 2 to 5,and the total number of carbon atoms is 3 to 7. Examples includeethylene glycol monomethyl ether (methyl cellosolve), ethylene glycolmonoethyl ether (ethyl cellosolve also known as ethoxyethanol), butylcellosolve, ethylene glycol monoalkyl ethers (cellosolves) such as2-isopropoxy-1-ethanol, 1-methoxy-2-propanol, 1-methoxy-2-butanol,3-methoxy-1-butanol, 4-methoxy-1-butanol, and 1-ethoxy-2-propanol. Anexemplary keto-alcohol is diacetone alcohol. Fluorinated alcohols suchas 2,2,3,3-tetrafluoropropanol are also useful.

Preferred for the aliphatic hydrocarbon solvents are n-hexane,cyclohexane, methylcyclohexane, ethylcyclohexane, cyclooctane,dimethylcyclohexane, n-octane, iso-propylcyclo-hexane andt-butylcyclohexane, among which ethylcyclohexane and dimethylcyclohexaneare most preferable.

Cyclohexanone is typical of the ketone solvent.

In the practice of the invention, alkoxyalcohols such as ethylene glycolmonoalkyl ethers are preferred. Preferred among these are ethyleneglycol monoethyl ether, 1-methoxy-2-propanol, 1-methoxy-2-butanol, etc.Also preferred is a mixture of these solvents, for example, acombination of ethylene glycol monoethyl ether and 1-methoxy-2-butanol.Fluorinated alcohols are also preferable.

It is understood that the azo metal complex according to the inventionand the dye combined therewith such as a phthalocyanine dye arerespectively used as a mixture of two or more so as to meet theabove-mentioned values of n and k.

When a recording layer of an optical recording medium intended forrecording and reading at two wavelengths is formed of a mixture of twoor more dyes, the azo metal complex according to the invention and theother dye as typified by a phthalocyanine dye are preferably mixed suchthat the molar ratio of inventive azo metal complex/other dye may rangefrom 90/10 to 10/90.

A recording layer of the mix type mentioned just above may be formedusing a coating solution containing the two dyes in a predeterminedratio.

Also acceptable for the purpose of recording and reading at twowavelengths is a recording layer in which a layer of the azo metalcomplex according to the invention and a layer of the other dye aredisposed one on top of the other. The order of lamination may besuitably chosen while one layer usually has a thickness of about 20 to250 nm. A recording layer of the laminate type may be formed usingcoating solutions containing the respective dyes.

In the two layer structure using a recording layer of the laminate type,it is preferred that a lower recording layer (or first recording layer)containing an azo metal complex accommodating for short wavelength bedisposed on a substrate and an upper recording layer (or secondrecording layer) containing a phthalocyanine dye of formula (VI)accommodating for 780 nm be disposed thereon. It is preferred hereinthat the lower recording layer is thinner than the upper recording layerand that the lower and upper recording layers are formed such that thethickness ratio of lower layer/upper layer may range from 1/10 to 1/1.

One structural embodiment of the optical recording disc having such arecording layer accommodating for two wavelengths or a short wavelengthon a substrate is illustrated in FIG. 2. FIG. 2 is a fragmentalsectional view. The optical recording disc 1 shown in FIG. 2 is a closecontact type optical recording disc which has a recording layer and areflective layer disposed in close contact therewith and enables readingaccording to the CD standard. As illustrated, the optical recording disc1 includes a recording layer 3 containing a dye in the form of an azometal complex compound according to the invention, which is formed onthe surface of a substrate 2, a reflective layer 4 in close contact withthe recording layer 3, and a protective film 5.

The recording layer 3 may be of the two wavelength accommodating modeincluding the mix type and the laminate type, of the short wavelengthaccommodating mode using an azo metal complex as a major component, orof the conventional wavelength accommodating mode.

The substrate 2 is in a disc form and, to enable write and read from theback surface of the substrate 2, is preferably formed of a resin orglass material which is substantially transparent (and preferably has atransmittance of at least 88%) to writing and reading light (typicallylaser light having a wavelength of about 500 nm to about 900 nm, furthertypically about 500 to about 700 nm, still further typically about 630to about 690 nm, most typically about 635 nm to about 680 nm, laserlight having a wavelength of about 680 to about 900 nm, andsemiconductor laser light having a wavelength of about 770 nm to about900 nm, further typically about 770 to 830 nm; especially 650 nm and 780nm). With respect to dimensions, the disc has a diameter of about 64 mmto about 200 mm and a thickness of about 1.2 mm.

On the surface of the substrate 2 where the recording layer 3 is formed,a groove 23 is formed for tracking purposes, as shown in FIG. 2. Thegroove 23 is preferably a continuous spiral groove having a depth of 0.1to 0.25 μm, a width of 0.35 to 0.60 μm for the mix type, the shortwavelength accommodating mode and the conventional wavelengthaccommodating mode and 0.35 to 0.80 μm for the laminate type and agroove pitch of 1.5 to 1.7 μm. Such groove configuration enablesgood-enough tracking signals to be obtained without a lowering of thereflection level of the groove area. It is particularly important tolimit the groove width to 0.35 to 0.80 μm or 0.35 to 0.60 μm. A groovewidth of less than 0.35 μm makes it difficult to obtain tracking signalsof sufficient magnitude, resulting in an increased jitter even whentracking is slightly offset during recording. A too greater groove widthhas a likelihood that read signals are subject to waveform distortion.

The substrate 2 is preferably formed of resins, typically thermoplasticresins such as polycarbonate resins, acrylic resins, amorphouspolyolefins, TPX and polystyrene resins. Using these resins, thesubstrate can be prepared by well-known techniques such as injectionmolding. Preferably, the groove 23 should be formed simultaneously withthe molding of the substrate 2. Alternatively, a resin layer having thegroove 23 may be formed by 2P or other methods after the fabrication ofthe substrate 2. Also, a glass substrate is useful as the case may be.

As shown in FIG. 2, the recording layer 3 deposited on the substrate 2is formed using the above-mentioned dye-containing coating solution,preferably by spin coating as mentioned previously. Spin coating may becarried out from the inner to the outer periphery under conventionalconditions while the number of revolutions is adjusted between 500 rpmand 5,000 rpm.

Preferably, the thus formed recording layer 3 has an as-dried thicknessof 500 to 3,000 Å (50 to 300 nm) for the mix type, the short wavelengthaccommodating mode and the conventional wavelength accommodating mode. Adeparture from this range gives rise to a reflectance drop, rendering itdifficult to read according to the CD standard. A very high degree ofmodulation is obtained when the thickness of the tracking area of therecording layer 3 within the groove 23 is kept at 1,000 Å (100 nm) ormore, especially, at 1,300 to 3,000 Å (130 to 300 nm).

For the laminate type, each recording layer preferably has an as-driedthickness of 200 to 2,500 Å (20 to 250 nm) as previously mentionedbecause better reading is expectable. Also preferably the thickness ofthe tracking area of the recording layer 3 within the groove 23 is keptat 500 Å (50 nm) or more, especially, at 500 to 800 Å (50 to 80 nm).Further, in the embodiment of the two layer structure having the azometal complex dye according to the invention contained in the lowerlayer as previously mentioned, better recording and reading at 780 nm isexpectable in the CD-RII mode by controlling the thickness of the upperand lower layers as mentioned above.

The thus formed recording layer 3 should preferably have n=1.8 to 2.3and k=0.02 to 0.20 at 650 nm and n=1.8 to 2.6 and k=0.02 to 0.30 at 780nm when it is a recording layer of the dye mix type accommodating fortwo wavelengths. The recording layer 3 should preferably have n=1.8 to2.6 and k=0.02 to 0.20 at 650 nm and n=1.8 to 2.6 and k=0.02 to 0.15 at780 nm when it is a recording layer of the laminate type accommodatingfor two wavelengths. By controlling n and k within these ranges, betterrecording and reading at two wavelengths is possible. Especially at theconventional wavelength of about 780 nm, recording and reading complyingwith the Orange Book standard is possible.

In the mode accommodating for a short wavelength of about 650 nm or aconventional wavelength of about 780 nm, the recording layer shouldpreferably have a coefficient of extinction k (imaginary part of acomplex index of refraction) of 0 to 0.20 at the wavelengths ofrecording light and reading light. With k greater than 0.20, nosatisfactory reflectance is obtained. Further, the recording layershould preferably have an index of refraction n (real part of a complexindex of refraction) of at least 1.8. With n less than 1.8, signalmodulation would be too small. No upper limit is imposed on n althoughit is usually about 2.6 for convenience of synthesis of dye compoundsand other reasons.

It is noted that n and k of a recording layer are determined bypreparing a test sample in which a recording layer is formed on a giventransparent substrate to a thickness of about 40 to 100 nm, for example,under practical conditions, and measuring the test sample forreflectance through the substrate or on the recording layer side. Thereflectance is measured in a specular reflection mode (of the order of5°) using the wavelength of recording light and reading light. Thesample is also measured for transmittance. From these measurements, nand k are calculated according to ISHIGURO Kozo, “Optics,” KyoritsuPublishing K.K., pages 168-178, for example.

It is understood that a recording layer has n and k which correspond ton and k of a particular dye used therein.

As shown in FIG. 2, the reflective layer 4 is formed on the recordinglayer 3 in direct contact relation thereto. Preferably, the reflectivelayer 4 is formed of a high-reflectance metal or alloy such as Au, Cu,Al, Ag and AgCu. The reflective layer 4 preferably has a thickness of atleast 500 Å, and may be formed as by evaporation and sputtering. Theupper limit of thickness is not critical, although it is preferablyabout 1,200 Å or less when cost, production time and other factors aretaken into account. Then the reflective layer itself has a reflectanceof at least 90%, and the reflectance of an unrecorded area of the mediumthrough the substrate is satisfactory and can be at least 60%,especially at least 70% at the conventional wavelength of about 780 nmin the case of the two wavelength accommodating mode.

As shown in FIG. 2, the protective layer 5 is formed on the reflectivelayer 4. The protective layer 5 is formed of various resin materialssuch as UV-curable resins, for instance, and usually has a thickness ofabout 0.5 μm to about 100 μm. The protective layer 5 may be in a layeror sheet form. The protective layer 5 may be formed by conventionalprocesses such as spin coating, gravure coating, spray coating anddipping.

Recording or additional writing may be carried out on the opticalrecording disc 1 of such construction by directing recording lighthaving a wavelength of 650 nm or 780 nm, for example, in pulse form tothe recording layer 3 through the substrate 2 to form an irradiated spotwhere optical reflectance is changed. Upon irradiation of recordinglight, the recording layer 3 absorbs light so that it is heated whilethe substrate 2 is heated at the same time. As a result, the materialsof the recording layer such as the dyes melt or decompose in thevicinity of the interface between the substrate 2 and the recordinglayer 3, probably applying pressure to that interface to deform thebottom and side walls of the groove.

The azo metal complex compounds according to the invention may also beused in the recording layer of write-once digital video discs (DVD-R)adapted to carry out recording and reading at a short wavelength ofabout 635 nm One exemplary construction of the disc is shown in FIG. 3.FIG. 3 is a fragmental sectional view.

The optical recording disc 10 shown in FIG. 3 is an optical recordingdisc complying with the DVD standard, which is obtained by adhesivelyjoining two discs of the same structure as the optical recording disc 1,with their protective films 15 and 25 faced each other. The adhesiveused herein may be a thermosetting resin or the like, and an adhesivelayer 50 has a thickness of about 10 to 200 μm. The substrates (whichare generally formed of a polycarbonate resin) each have a thickness of0.6 mm. On one substrate 12 having a groove 123 formed therein, arecording layer 13, a reflective layer 14 and a protective film 15 as inFIG. 2 are successively formed. On another substrate 22 having a groove223 formed therein, a recording layer 23, a reflective layer 24 and aprotective film 25 are similarly formed. They are then joined togetheras mentioned above.

The substrates accord with the above-described one for CD, and theirgroove has a depth of 600 to 2,000 Å, a width of 0.2 to 0.5 μm, and apitch of 0.6 to 1.0 μm.

The recording layer has a thickness of 500 to 3,000 Å and its complexindex of refraction at 635 nm consists of n=1.8 to 2.6 and k=0.02 to0.20.

EXAMPLE

Examples of the invention are given below, together with ComparativeExamples, by way of illustration.

Example 1

A salt-forming dye: Compound D-1 was used as a dye to form an opticalrecording layer. On a polycarbonate resin substrate of 120 mm indiameter and 1.2 mm thick having a pregroove (depth 0.16 μm, width 0.45μm, and groove pitch 1.6 μm), a recording layer containing the dye wasformed to a thickness of 1,800 Å (180 nm) by spin coating. The coatingsolution used herein was a 1.0 wt % 2,2,3,3-tetrafluoropropanolsolution. Next, a reflective layer of Au was formed on the recordinglayer to a thickness of 850 Å by sputtering, and a transparentprotective film of a UV-curable acrylic resin (5 μm thick) was formedthereon, fabricating a disc (see FIG. 2).

Using a laser having an oscillation wavelength of 780 nm, signals wererecorded and read from the thus fabricated optical recording disc sampleNo. 101 at a linear velocity of 1.2 m/s for evaluating optimum recordingpower (Po), reflectance, modulation, and jitter. These measurementssatisfied the Orange Book standard.

Further the sample was examined for light resistance. Light resistancewas examined by exposing the sample to a xenon lamp at 80,000 lux (XenonFadeometer manufactured by Shimazu Mfg. K.K.) for 40 hours, andmeasuring the jitter of the disc. The jitter remained unchanged. Areliability test was carried out under conditions of 80° C. and RH 80%for 100 hours, finding no deterioration.

Samples were fabricated as sample No. 101 except that salt-forming dyes:Compounds D-2 to D-20 were used as the recording layer dye instead ofthe salt-forming dye: Compound D-1. These samples are designated sampleNos. 102 to 120. Using a mixture of D-4 and D-12, sample No. 121 wasalso fabricated. As a result, these samples also showed satisfactoryproperties.

Of the salt-forming dye compounds, those compounds having indoleninecyanine dye ions as the counterion allows a choice of solvent from awider range in preparing the coating solution as compared with thethiazoline and oxazoline systems. Coating solutions could be readilyprepared using cellosolve solvents such as ethyl cellosolve.

Example 2

An optical recording disc was fabricated using an azo metal complex:Compound 1 as a dye to form a recording layer. On a polycarbonate resinsubstrate of 120 mm in diameter and 0.6 mm thick having a pregroove(depth 0.10 μm, width 0.42 μm, and groove pitch 0.74 or 0.8 μm), arecording layer containing the dye was formed to a thickness of 1,300 Å(130 nm) by spin coating. The coating solution used herein was a 1.0 wt% 2,2,3,3-tetrafluoropropanol solution. Next, a reflective layer of Authick was formed on the recording layer to a thickness of 850 Å bysputtering, and a transparent protective film (5 μm thick) of aUV-curable acrylic resin was formed thereon. Two disc samples formed inthis way were mated such that the protective films were joined withadhesive, obtaining a disc (see FIG. 3).

This is designated sample No. 201.

Samples we re fabricated as sample No. 201 except that Compounds 3, 4,6, 9 to 17, 21, 22, C-1, C-2, C-5to C-12, and C-16 to C-31 as shown inTable 7 were used as the recording layer dye instead of Compound 1.These samples are designated sample Nos. 202 to 241.

The thus fabricated sample Nos. 201 to 241 were examined for variouscharacteristics by recording signals at a linear velocity of 3.8 m/swith a laser beam of 635 nm and then reading the signals at a linearvelocity of 3.8 m/s with a laser beam of 635 nm. The lens had anumerical aperture (NA) of 0.60. The characteristics examined includedreflectance, modulation (Mod.), jitter, and optimum recording power(Po).

The results are shown in Tables 6 and 7.

TABLE 6 Sample Recording Reflectance Mod. Jitter No. layer dye (%) (%)(%:σ/Tw) P0 (mW) 201 Compound 1 58 70 8 8.2 202 Compound 3 57 64 8 8.3203 Compound 4 56 63 8 8.3 204 Compound 6 50 55 8.7 9.0 205 Compound 951 60 8.3 8.3 206 Compound 10 50 55 8.7 8.8 207 Compound 11 50 57 9.08.8 208 Compound 12 57 68 9.0 11.0 209 Compound 13 57 69 9.0 11.0 210Compound 14 63 70 9.3 11.3 211 Compound 15 62 71 9.0 11.5 212 Compound16 50 56 9.2 11.2 213 Compound 17 55 64 9.2 11.3 214 Compound 21 56 55 88.3 215 Compound 22 55 66 7.8 8.4 216 Compound C-1 50 55 8.3 8.5 217Compound C-2 56 57 8.7 9.0 218 Compound C-5 57 68 8.2 8.5 219 CompoundC-6 60 70 8.0 8.2 220 Compound C-7 61 62 7.8 8.3 221 Compound C-8 55 637.6 8.4 222 Compound C-9 55 63 7.7 8.5 223 Compound C-10 50 64 7.9 8.6

TABLE 7 Sample Recording Reflectance Mod. Jitter No. layer dye (%) (%)(%:σ/Tw) P0 (mW) 224 C-11 51 60 8.0 8.1 225 C-12 52 62 7.8 8.3 226 C-1655 67 7.6 8.5 227 C-17 53 64 8.1 8.0 228 C-18 55 60 8.2 8.3 229 C-19 5955 8.6 9.0 230 C-20 60 57 8.8 9.3 231 C-21 54 60 7.5 9.0 232 C-22 50 658.0 8.5 233 C-23 53 65 7.8 7.8 234 C-24 48 65 7.8 7.5 235 C-25 46 60 8.07.2 236 C-26 47 63 7.8 7.8 237 C-27 47 60 8.5 7.9 238 C-28 50 65 7.9 8.2239 C-29 53 65 8.0 8.1 240 C-30 55 60 8.3 7.9 241 C-31 58 58 8.3 9

It is evident from Tables 6 and 7 that the reflectance, modulation, andjitter are satisfactory.

It is evident that among the azo metal complexes according to theinvention, discs using VO complexes of compounds of formula (V) showsignificantly improved characteristics.

Sample Nos. 201 to 241 were further examined for light resistance. Lightresistance was examined by exposing the sample to a xenon lamp at 80,000lux (Xenon Fadeometer manufactured by Shimazu Mfg. K.K.) for 40 hours,and measuring the jitter of the disc. For all the samples, the jitterremained unchanged.

A reliability test was carried out under conditions of 80° C. and RH 80%for 100 hours, finding no deterioration.

Of the salt-forming dye compounds, those compounds having indoleninecyanine dye ions as the counterion allows a choice of solvent from awider range in preparing the coating solution as compared with thethiazoline and oxazoline systems. Coating solutions could be readilyprepared using cellosolve solvents such as ethyl cellosolve.

Comparative Example 1

A disc sample was fabricated as in Example 1 except that the coatingsolution used contained a 1:1 mixture of Metal Complex B which was anintermediate in the synthesis of Compound D-1 in Synthesis Example 14and a ClO₄ salt of Cyanine Dye B-39. Upon application, some crystals ofMetal Complex B remained undissolved in the coating solution, and thefilter was clogged. The tests on the thus fabricated sample showedinsufficient light resistance and substantial deterioration of jitter. Areliability test also showed substantially deteriorated modulation andjitter.

Comparative Example 2

A disc sample was fabricated as in Example 2 except that the coatingsolution used contained a 1:1 mixture of Metal Complex A which was anintermediate in the synthesis of Compound C-24 in Synthesis Example 11and a ClO₄ salt of Cyanine Dye B-9. Upon application, some crystals ofMetal Complex A remained undissolved in the coating solution and thefilter was clogged. The tests on the thus fabricated sample showedinsufficient light resistance and substantial deterioration ofmodulation and jitter. In a reliability test, several parameters couldnot be measured because of the substantially deteriorated modulation.

Comparative Example 3

A disc sample was fabricated as in Example 1 using a bonded compoundwhich was obtained by using a chromium family azo complex (a-1), shownbelow, disclosed in JP-B 51182/1991 and a heptamethine family cyaninedye (b-2), shown below, and bonding them in accordance with the methodof JP-A 51182/1991. The sample was examined as in Example 1. The resultscould not meet the Orange Book standard.

Using a sample having only the recording layer formed thereon, itsabsorption spectrum was measured. It showed absorption characteristicsas shown in FIG. 2 of JP-A 51182/1991. The measurement of n and k at 780nm gave n=2.40 and k=0.8, indicating a failure to provide satisfactorymedium properties.

Example 3

A mixture of an azo metal complex: Compound 2 and Phthalocyanine Dye A-3in a weight ratio of 1:1 was used as a dye to form an optical recordinglayer On an polycarbonate resin substrate of 120 mm in diameter and 1.2mm thick having a pregroove (depth 0.14 μm, width 0.50 μm, and groovepitch 1.6 μm), a recording layer containing the dye was formed to athickness of 2,000 Å (200 nm) by spin coating. The coating solution usedherein was a 2 wt % 2-ethoxyethanol solution. Next, a reflective layerof Au was formed on the recording layer to a thickness of 850 Å bysputtering, and a transparent protective film of a UV-curable acrylicresin (5 μm thick) was formed thereon, fabricating a disc (see FIG. 2).

As previously described, Compound 2 had λmax of 620 nm as measured on athin film sample of 50 nm thick, and its n and k at 650 nm as measuredby the aforementioned method were n=2.35 and k=0.02.

Also as previously described, Dye A-3 had λmax of 725 nm as measured ona thin film sample of 80 nm thick, a half band width of 125 nm, n=2.4and k=0.10.

The thus fabricated optical recording disc sample No. 401 was examinedfor optimum recording power (Po), reflectance, modulation, and jitter byrecording signals at a linear velocity of 1.2 m/s using a laser havingan oscillation wavelength of 780 nm and reading the signals using alaser having an oscillation wavelength of 780 nm and a laser having anoscillation wavelength of 650 nm. These results are shown below.

Examination with 780-nm laser

optimum recording power 7.5 mW

reflectance 70%

modulation 63%

jitter 22 ns

Examination with 650-nm laser

reflectance 30%

modulation 62%

jitter 25 ns

The sample was further examined for light resistance. Light resistancewas examined by exposing the sample to a xenon lamp at 80,000 lux (XenonFadeometer manufactured by Shimazu Mfg. K.K.) for 40 hours, andmeasuring the jitter of the disc. The jitter remained unchanged.

Example 4

A disc sample No. 302 was fabricated as was sample No. 301 in Example 3except that the azo metal complex: Compound 2 was replaced by Compound5. It was similarly examined, with the results shown below.

Examination with 780-nm laser

optimum recording power 7.5 mW

reflectance 68%

modulation 63%

jitter 24 ns

Examination with 650-nm laser

reflectance 30%

modulation 62%

jitter 25 ns

The sample was further examined for light resistance. Light resistancewas examined by exposing the sample to a xenon lamp at 80,000 lux (XenonFadeometer manufactured by Shimazu Mfg. K.K.) for 40 hours, andmeasuring the jitter of the disc. The jitter remained unchanged.

Example 5

Disc sample Nos. 303 to 317 were fabricated as was sample No. 301 inExample 3 except that the azo metal complex: Compound 2 was replaced byCompounds 1, 3, 7, 8, 18, 20, C-3, C-4, C-6, and C-13 to C-18. They weresimilarly examined. They showed satisfactory results equivalent to thoseof sample No. 301 in Example 4 and sample No. 302 in Example 5.

Example 6

An optical recording disc was fabricated as in Example 3 except that arecording layer of the lamination type was formed instead of the mixtype.

A lower recording layer of 500 Å thick was formed on a substrate byapplying a 0.8 wt % 2,2,3,3-tetrafluoropropanol solution of an azo metalcomplex: Compound 8 by spin coating, and drying at 60° C. for 3 hours.

An upper recording layer of 1,000 Å thick was formed on the lowerrecording layer by applying a 2.0 wt % ethylcyclohexane solution ofPhthalocyanine Dye A-3 by spin coating, and drying at 60° C. for 3hours.

On the recording layer of the two-layer structure, a reflective layer ofAu was formed to a thickness of 850 Å by sputtering, and a UV-curableacrylic resin was coated thereon to a thickness of 5 μm as a protectivefilm.

A disc sample No. 601 was fabricated in this way.

Disc sample No. 601 was examined as in Example 3, with the results shownbelow.

Examination with 780-nm laser

optimum recording power 6.0 mW

reflectance 68%

modulation 65%

jitter 22 ns

Examination with 650-nm laser

reflectance 30%

modulation 60%

jitter 25 ns

Sample No. 601 was examined for light resistance as in Example 4. Thejitter remained unchanged, indicating satisfactory light resistance.

Comparative Example 4

Using an azo cobalt dye of the type disclosed in JP-B 15682/1995, shownbelow, an optical recording disc was fabricated as in Example 2. Thedisc was examined for various characteristics. It showed a reflectanceof 49%, a modulation of 60%, a jitter of 8.5% (σ/Tw), and an optimumrecording power of 12.0 mW.

This sample showed apparently inferior characteristics to the sample ofExample 2.

Comparative Example 5

Using a nickel complex of an azo compound of the type disclosed in JP-A156408/1996, shown below, an optical recording disc was fabricated as inExample 2. The disc was examined for various characteristics. It showeda reflectance of 50%, a modulation of 48%, a jitter of 9.0% (σ/Tw), andan optimum recording power of 12.0 mW.

This sample showed apparently inferior characteristics to the sample ofExample 2.

Example 7

An optical recording disc was fabricated using a mixture of an azo metalcomplex: Compound C-6 and a ClO₄ salt of Cyanine Dye B-11 in a weightratio of 80:20 as a dye to form a recording layer.

On a polycarbonate resin substrate of 120 mm in diameter and 0.6 mmthick having a pregroove (depth 0.16 μm, width 0.30 μm, and groove pitch0.8 μm), a recording layer containing the dyes was formed to a thicknessof 100 nm by spin coating. The coating solution used herein was a 0.9 wt% 2,2,3,3-tetrafluoropropanol solution. Except these points, a disc wasfabricated as in Example 2 (see FIG. 3).

This is designated disc sample No. 701. The thus fabricated sample wasexamined for recording characteristics as in Example 2.

For samples using different combinations of the azo metal complex withthe cyanine dye (used as a ClO₄ salt in all samples), the type of dyeand mixing ratio are shown in Table 8 together with the results oftests.

TABLE 8 Azo metal Reflec- Sample com- Cyanine Mixing tance Mod. JitterPo No. plex dye ratio (%) (%) (%, s/Tw) (mW) 701 C-6   B-11 80:20 55 618.5 10 702 C-6  B-1 80:20 51 60 8.8 10.2 703 C-6  B-2 90:10 50 61 8.7 10704 C-6  B-5 80:20 53 62 8.7 10 705 C-5  B-5 80:20 51 61 8.8 10.3 706C-5  B-7 90:10 48 60 8.5 10 707 C-21 B-8 80:20 52 63 8.5 10.5 708 C-21 B-10 80:20 55 60 8.4 10.3 709 C-30 B-8 80:20 51 62 8.1 10 710 C-29 B-13 80:20 48 61 8.8 10.2

It is evident from Table 8 that the reflectance, modulation and jitterare all satisfactory. As in Example 2, light resistance was examined andthe reliability test was carried out. As a result, the jitter remainedunchanged, indicating excellent light resistance. No deteriorationoccurred in the reliability test.

There has been described an optical recording medium using as the lightabsorbing dye an azo metal complex compound having improved solubility,light resistance and reliability and providing improved characteristicsincluding a good balance of recording sensitivity, reflectance andmodulation, a high recording sensitivity, and a minimal jitter.

Using an azo metal complex compound for the short wavelength operationin combination with a dye having absorption on a long wavelength side,an optical recording medium of the two wavelength accommodating type canbe formed.

What is claimed is:
 1. An optical recording medium comprising arecording layer containing an azo oxovanadium metal complex between anazo compound of the following formula (III) and oxovanadium;A—N═N—B  (III) wherein A is an aromatic ring group having an activehydrogen-bearing group at a position adjacent to the diazo group or anitrogenous heteroaromatic ring group having therein anoxovanadium-coordinatable nitrogen atom at a position adjacent to thecarbon atom in the ring attached to the diazo group; and B is anaromatic ring group having an active hydrogen-bearing group at aposition adjacent to the diazo group.
 2. The optical recording medium ofclaim 1 wherein A in formula (III) is an aromatic ring group having anactive hydrogen-bearing group at a position adjacent to the diazo group.3. The optical recording medium of claim 1 wherein said recording layercontains a second light-absorbing dye having different opticalproperties from said azo metal complex, and recording/reading operationis carried out with light having a first wavelength of 630 to 690 nm andlight having a second wavelength of 770 to 830 nm.
 4. The opticalrecording medium of claim 3 wherein recording is carried out with lighthaving the second wavelength and reading is carried out with lighthaving the first and second wavelengths.
 5. The optical recording mediumof claim 3 wherein said recording layer is disposed on a substrate, inwhich said azo metal complex has a complex index of refraction at 650 nmwhose real part n is 1.8 to 2.6 and whose imaginary part k is 0.02 to0.20, and said second light-absorbing dye has a complex index ofrefraction at 780 nm whose real part n is 1.8 to 2.6 and whose imaginarypart k is 0.02 to 0.30 and forms a thin film whose absorption spectrumhas a half band width of up to 170 nm.
 6. The optical recording mediumof claim 3 wherein said second light-absorbing dye is a phthalocyaninedye of the following formula (VI):

wherein M is a center atom; X₁, X₂, X₃ and X₄, which may be the same ordifferent, are halogen atoms; p1, p2, p3 and p4 are 0 or integers of 1to 4, p1+p2+p3+p4 is equal to 0 to 15; Y₁, Y₂, Y₃ and Y₄ which may bethe same or different, are oxygen atoms or sulphur atoms: Z₁, Z₂, Z₃ andZ₄, which may be the same or different, are alkyl groups having at least4 carbon atoms, alicyclic hydrocarbon groups, aromatic hydrocarbongroups or heterocyclic groups; q1, q2, q3 and q4 are 0 or integers of 1to 4, they are not equal to 0 at the same time, and q1+q2+q3+q4 is equalto 1 to
 8. 7. The optical recording medium of claim 1 wherein therecording layer is constructed of at least two layers by laying on afirst recording layer containing said azo metal complex a secondrecording layer containing a second light-absorbing dye having differentoptical properties from said azo metal complex.
 8. The optical recordingmedium of claim 7 wherein said azo metal complex has a complex index ofrefraction at 650 nm whose real part n is 1.8 to 2.6 and whose imaginarypart k is 0.02 to 0.20, and said second light-absorbing dye has acomplex index of refraction at 780 nm whose real part n is 1.8 to 2.6and whose imaginary part k is 0.02 to 0.15 and forms a thin film whoseabsorption spectrum has a half band width of up to 170 nm, and therecording layer constructed of at least two layers is disposed on asubstrate.
 9. The optical recording medium of claim 7 wherein the firstrecording layer is disposed on the substrate, and the second recordinglayer is disposed on the first recording layer.
 10. The opticalrecording medium of claim 9 wherein said first recording layer and saidsecond recording layer each have a thickness of 20 to 250 nm, and thethickness of said first recording layer divided by the thickness of saidsecond recording layer is from 0.1 to
 1. 11. The optical recordingmedium of claim 1, wherein a counter cation is a cyanine cationaccording to formula (II) of claim
 1. 12. An optical recording mediumcomprising a recording layer containing an azo metal complex obtained bycombining at least one of an azo compound of the following formula (IV)and a compound of the following formula (V) with a metal compound;

wherein X is an active hydrogen-bearing group, R¹ and R² each are analkyl group, the total number of carbon atoms in R¹ and R² is from 2 to8, R is a nitro group, and n is equal to 0 or
 1. 13. The opticalrecording medium of claim 12 wherein said azo metal complex is a metalcomplex with oxovanadium or cobalt.
 14. The optical recording medium ofclaim 7 wherein said azo metal complex is a metal complex of thecompound of formula (V) with oxovanadium or cobalt.
 15. The opticalrecording medium of claim 12, wherein a counter cation is a cyaninecation according to formula (II) of claim 1.